The Big Picture: Star Wars Episode II: Attack of the Clones (PG)

Here we go again. If anything to do with the Star Wars franchise can be called good news then it's that this latest prequel is at least an improvement on The Phantom Menace (1999). How exactly could it have been worse? Well, they could have given a starring role to Jar Jar Binks, one of the most lavishly unamusing creatures ever to pass across a movie screen, but I can't see how anything short of doubling its length could make Episode II as intolerable as Episode I. True, Jar Jar is back, but he's been kicked upstairs, and so too is that bat-faced troll Yoda, whose cutely inverted sentences merit a kicking, period.

Attack of the Clones, as thinly dramatised as it is, does not move with quite the torturing leadenness of the previous film, its effects seem less tinny and there is one acting performance that manages to carry some small authority and weight. Step forward Christopher Lee as the renegade Jedi knight Dooku, turning his chilly composure to advantage and creating ripples of danger on the film's otherwise placid surface. It's a role not so different from his evil Saruman in The Lord of The Rings, but in a movie where the acting remains strictly one-emotion-at-a-time Lee becomes a positive beacon of relief from the central performers.

Take Ewan McGregor as Obi-Wan Kenobi, still twisting his voice into a ridiculous, overarticulated impersonation of British cool that's meant to sound like Alec Guinness: it doesn't, and never could. McGregor's stiltedness is bad enough, but more ruinous to the film's cause are the two romantic leads. Natalie Portman as Queen Amidala suffered horribly in Phantom Menace, and while the makeup has been toned down a shade, the wardrobe people seem determined to whip through as many hideous costume changes as they can for her within the space of two-and-half-hours. It makes Liz Taylor's gear in Cleopatra look winningly understated. When Portman's hair isn't shrouded under some awful headdress it's been teased into an advert for the latest fad in tonsorial topiary. What is it about outer space that encourages stylists to believe people should have silly haircuts?

Poor old Hayden Christensen, playing Anakin Skywalker – and Amidala's suitor – has been dealt a cruel twin blow by having not just a ponytail but a sad little braid curling over his shoulder. Hard to know what sort of character to project with a hairstyle like that, and Christensen struggles with what ought to be the pivotal role: this, remember, is the youth destined to become Darth Vader, and we are meant to detect in him warning signs of his later conversion to evil. Not so far. Christensen can't manage anything stronger than a teenage strop as he rails against his mentor, Obi-Wan: "He never listens. He just doesn't understand. It's not fair." Were Kevin and Perry not available?

In truth, it would be difficult for any actor to instil grace and conviction into the lines that George Lucas has written. This writer-director-producer really is a phenomenon: one could scarcely tell from his vacuous, antiphonal dialogue that he has spent time in the company of human beings at all. The screenplay is co-credited to him and Jonathan Hales; between them they haven't succeeded in dreaming up a single interesting line. There's an occasional stab at humour amid the drowning portentousness, but nothing that would raise a smile, or even a smirk. This film wants to dazzle us, only without having to enquire too closely into the human drama of desire, ambition, fear. It's not that George Lucas has no imagination; it's just that what he does imagine is so very, very boring.

There's a plot of sorts. Amidala, now a senator, is trying to preserve the Republic against breakaway factions, for which pains she has become a target for assassination. The authorities depute Obi-Wan and Anakin to be her protectors, and soon enough they're crossing paths and lightsabers with a roving bounty hunter and a genetically engineered army – the "clones" of the title – marshalled by that apostate Jedi, the thin white Dooku.

The film lurches from one set-piece fight to another, from one chase sequence to the next, offering us spectacle in the hope that we won't notice the paltriness of its moral conflict. You may care to admire the nocturnal cityscape of Coruscant with its airborne, crisscrossing traffic, impressive in its way, though something you may have already seen in Luc Besson's sci-fi epic The Fifth Element a few years back.

The climactic arena fight is even more flagrant in its borrowing – you can almost sense Lucas's disappointment that he didn't make Gladiator. Ridley Scott wasn't shy of bolting on the special effects, of course, but at least we're never in doubt that Nubian archers on spike-wheeled chariots and sabre-toothed tigers on chains would be, like, scary. The mutant beasts that menace the humans in Attack of the Clones are so obviously a product of the lab you suddenly get an idea of how a 13-year-old boy might feel zapping monsters in the video arcade. How long, I wonder, did those actors spend shaking their lightsabers at thin air?

It would be pleasant to report that refuge can be found in the more reflective passages, but these simply expose Lucas's poverty as a writer – the love scenes between Amidala and Anakin are so excruciating you immediately want to get back to the whizz-bangs. Will any of this matter to the fans? Revenues from The Phantom Menace ($431m at the American box-office) suggest it won't.

The film critic David Thomson has expressed doubts as to whether Lucas can keep offering shoddy work and be successful, but the franchise seems to generate its own momentum. The Star Wars habit may have become ingrained. They'll be counting the cash at the Skywalker Ranch – you'll just be counting the slow minutes to the end of this movie.